Spurred by concern that the ongoing eruption of Scather's volcano would cause the crops to fail and famine to descend on her town, the Gynarch led two-thirds of her available troops to deal with the situation. She knew the way well from having delivered tribute to the dragon in the past. On arrival, she joined forces with Mareth the paladin and a group of twenty wereboars who had been driven from their dens in the tunnels beneath the volcano by the arrival of the fire giants.
The approach of the Gynarch's troops was noted by the Iron Dragon, a rival of Scather's eager to seize this opportunity to destabilize the giants' grip on the dragon's lair and claim its hoard. The dragon flew east to the elven town it controlled along with the wizard Slumath, and came back with thirty elven heroes harnessed to its body, plus Slumath and forty griffon-riders flying alongside.
The Gynarch led her men and horses up the side of the volcano, and then down again into its crater. They saw that the giants led by King Snurre had built a fortress out of the cone produced by this latest eruption, near the center of this caldera. There are some areas of rubble and fumaroles between the edge of the caldera, but otherwise it's a flat plain:
As these troops drew near to the giants' fortress, the Iron Dragon and griffon-riders also approached. The Gynarch rode towards them with ten of her heavy cavalry, waving a flag of parley. The Iron Dragon met them and an arrangement was quickly established: the dragon would claim Scather's hoard and lair, in exchange for helping stop the river that had been diverted to create the eruption.
Battle was joined shortly after. The half-orc light cavalry breached the door of the giants' fortress, but were quickly defeated by hell hounds. The Iron Dragon landed on the middle level of the fortress, smashed open a door, roasted the gnolls inside, but then was promptly beaten to death by Queen Frumy's chambermaids after making the mistake of engaging them in melee. The wereboars scaled the walls and proved immune to the fire giants' weapons; not even being swept off the parapet and dropped 120 feet to the rocks below slowed them down for long.
Meanwhile, Slumath and his elven allies made their way invisibly through the tunnels to the caverns beneath the volcano. They found a huge, unguarded cavern lined with gold, which Scather had melted into place using his acid breath; fourteen sizable gems studded this bricolage, and the fire giants had carved out some chunks and prepared them for transit. The invisibles continued on to the waterworks, where the famous Obmi had been advising King Snurre on the best way to engineer an eruption. The hell hounds in this room narrowly failed to scent the unseen visitors, who then revealed themselves by unleashing a hail of arrows and bolts from a wand of lightning that killed the unfortunate hounds. A lengthy battle broke out, during which Obmi and then a unit of giantesses were killed. Finally, Slumath figured out which moving part (neither the sluices nor the capstans, but the frammistans) he could zap in order to return the underground river to its usual course and stop the eruption.
Aboveground, the initial brunt of the fighting was borne by the Gynarch's half-orc troops, who took heavy casualties in their light armor. Once the heavy infantry and cavalry gained the interior of the fortress, however, they paid their own price in blood. The fire giants and giantesses descended to wreak havoc amongst the fighting men and women descending the massive stairs into the volcano's core. All were slain except the wereboars and the heroes Mareth and the Gynarch, then the archers and crossbowmen of Belltower added their numbers to the fray. One by one, the giants began to fall; the last survivor, King Snurre, slew half the wereboars with his enchanted flaming greatsword, but finally the Gynarch ended his reign.
With the last giants dead, Slumath and the Gynarch both honored the arrangements that had been tested and proven sound during half an hour of bloody pitched battle. The ten surviving wereboars retook possession of the tunnels near the volcano; the Gynarch, Mareth, and the surviving troops (30 longbowmen and 30 crossbowmen, plus the horses left outside the volcano) returned to Belltower after looting the bodies of the giants they had slain.
Slumath's survivors (20 elf heroes, 10 elf riders and their griffons) took over the volcanic fortress and the lair beneath it, including Scather's hoard and Obmi's gear. After the forces of Law had departed, they were approached by some of the goblins who had been employed by the fire giants. The goblins said that soon the frost giants would come and see why the eruption had stopped; they offered to act as go-betweens to arrange a deal. Once charmed by Slumath, the would-be goblin emissaries explained that Obmi and the fire giants had been sent here to engineer an eruption that would block the sun so that the time of frost from dawn to dusk would come sooner, hastening the frost giants' ability to march on the Stronghold of First Principles. The goblins said that the giants would repay those who helped this happen, and punish those who stood in its way. Slumath decided that his village needed the sun to survive, and instead of throwing in his lot with the giants, sent messages to the Gynarch (and thus eventually to the Grey Company) of what he had learned.